The invention relates to a method for the preparation of highly heat resistant polyimide and polyisoindoloquinazoline dione relief structures in which radiation-sensitive soluble polymer precursors are applied to a substrate in the form of a film or foil, the film or foil is irradiated through negative patterns with actinic light, or with electrons, or by guiding a light, electron, ion or laser beam, the unirradiated film or foil portions are removed, and optionally the remaining irradiated portions are subsequently annealed. The invention also relates to the use of these relief structures.
Photo-structured polyimide and polyisoindoloquinazoline dione films are employed for example in the semiconductor industry as insulating and protective layers. Due to the severe cost pressure in the semiconductor sector, it is desirable to use low-cost materials and methods for the production of such films. This is why indirect photo-structuring of polyimide and polyisoindoloquinazoline dione films by means of conventional photo resists is not very appealing for the purpose mentioned. This method requires many steps and is very expensive.
From U.S. Pat. No. 3,957,512, a metnod related to that referred to above for the production of polyimide and polyisoindoloquinazoline dione relief structures is known. In this method, there are used as soluble polymer precursors polycondensation products of polyfunctional carbocyclic or heterocyclic compounds carrying radiation-sensitive radicals with diamines. The compounds carrying radiation-sensitive radicals here contain two carboxylic acid chloride groups suitable for condensation reactions and, partly in ortho- or peri-position thereto, radiation-sensitive groups bound to carboxyl groups in ester fashion. The diamines to be reacted with these compounds have at least one cyclic structure element.
The soluble polymer precursors are cross-linked during irradiation, being thus transformed into insoluble intermediate products. During annealing, these intermediate products undergo cyclization, with formation of highly heat resistant polyimides or polyisoindoloquinazoline diones.
The relief structures produced by the known method have proved successful in the practice. However, as a consequence of the manufacturing process in which acid chlorides are used, the polymer precursors used therein still contain a small residual chloride content, even after thorough purification. This residual chloride content may have a disturbing effect if the component requirements are extreme, as for instance in direct contact with P-N junctions in MOS components.
For the production of highly heat resistant polyimide and polyisoindoloquinazoline dione relief structures, a method is known further in which there are used as polymer precursors, addition products of olefinically unsaturated monoepoxides to carboxyl-group-containing polyaddition products of aromatic and/or heterocyclic tetracarboxylic acid dianhydrides and diamino compounds or diamino compounds having at least one ortho-positioned amido group (U.S. Pat. No. 4,311,785). As a result of the synthesis, however, these polymer precursors contain a relatively small proportion of photo-sensitive groups, resulting in a limited photo-sensitivity.
It is, therefore, an object of the invention to further improve the foregoing method for the preparation of polyimide and polyisoindoloquinazoline dione relief structures to the effect that in a cost-effective manner, high-purity and in particular, chloride-free relief structures can be produced using economically attractive exposure times.